This invention relates to using magnetic resonance techniques, especially electron spin resonance (ESR), to analyze substances in samples of the kind that include dissipative material, for example, animal tissue.
ESR has been used spectroscopically to determine the presence and concentration of particular substances in a sample under analysis. Typically a very small sample is subjected to a fixed radio frequency field in the so-called X band (e.g., 9.5 Gigahertz) and to a time-varying homogenous magnetic field. The resulting absorption spectrum is detected as an indication of the presence and concentration within the sample of substances whose electron spin resonances correspond to magnetic field intensities that fall within the detected spectrum for the particular fixed radio frequency being used. Typically the magnetic field is on the order of several thousand gauss and is provided by placing the sample between the poles of an electromagnet. The time variation in the magnetic field is accomplished by varying the current in a pair of sweep coils positioned respectively between each pole of the electromagnet and the sample.